\documentclass{standalone}
\usepackage{tikz}
\usepackage{ctex,siunitx}
\setCJKmainfont{Noto Serif CJK SC}
\usepackage{tkz-euclide}
\usepackage{amsmath}
\usetikzlibrary{patterns, calc}
\usetikzlibrary {decorations.pathmorphing, decorations.pathreplacing, decorations.shapes,}
\begin{document}
\small
\begin{tikzpicture}[>=latex,yscale=0.3,xscale=0.6]
  % \useasboundingbox(-2.65,-1.95)rectangle(0.65,1.35);
  \draw[->,  thick](0,0)--(4,0)node [below]{$a_1$};
  \draw[->,  thick](0,0)--(6,0)node [below]{$F_1$};
  \draw[->,  thick](0,0)--(2,4)node [left=0.1]{$a_2$};
  \draw[->,  thick](0,0)--(3,6)node [left=0.1]{$F_2$};
  \draw[dashed](6,4)--(2,4);
  \draw[dashed](9,6)--(3,6);
  \draw[dashed](6,4)--(4,0);
  \draw[dashed](9,6)--(6,0);
  \draw[<-, ultra thick](6,4)node [below]{$a$}--(0,0);
  \draw[<-, ultra thick](9,6)node [right]{$F_{\text{合}}$}--(0,0);
  \draw(-0.6,-0.8) rectangle (0.6,0.8);
\end{tikzpicture}
\end{document}